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Upgraded fuel injectors...lumpy idle

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I've upgraded my OEM fuel injectors to some ID1050x (thats a 90% increase?!)

Now, after my car warms up at about 85-87C it starts to ebb and flow with the idle from about 900rpm to as low as 520rpm.

I have the fuel injectors scaled to 960 at the moment; adjusted the warm up enrichment and cranking appropriately.

The car is an 04 STi and its on a stock OEM ECU.

Would I simply increase the idle parameters to a minimum of 900rpm, now that I have the new injectors? Cause that seems like the sensible thing to do, honestly.

Attached Files

If the only thing you've changed are the injectors to almost double the flow (why?), you may have a problem with lack of control at the very small opening they need to provide for the idle fuel demand.

There will be numerous things you can try, that others will need to advise on, but in the interim an idle speed increase may just increase the fuel demand enough to bring it into a controllable range.

For context, prior to the injectors I upgraded the whole fuel system. The injectors were the last thing that I upgraded.

I upgraded to a Radium duel fuel hanger system with two Walbro 450 fuel pumps, -8AN feed, and -6AN return line. Radium duel injector TGVs with appropriate fuel pulse dampers. Just wanted to focus on the 1050x (as these are the only ones connected to the car at the moment).

I'm building up to the power goal that I want but at the moment these are incremental steps.

In regard to the injectors I did also compensate by adjusting the cranking and warm-up enrichment tables to reflex the 2x increase in injector scale.

Perhaps a more specific question would be more simple and helpful in my case:

*How much does the injector latency contribute to idle tuning? For example, if there is a problem with idle hunting at low rpm would it be better to scale the inectors or adjust the latency?

What fuel pressure are you seeing at idle? I've seen it a lot with people oversizing their supply and injectors struggling to cope as they are running too high a base pressure causing all the latency values to be wrong.

Latency at idle is when it is most noticeable.

Do you still have the same base pressure in the fuel system? Increasing the pressure increases the amount of fuel injected for x period of injector duty, but it also increases the dead time of the injector before it opens and moves off the seat and starts to deliver fuel.

Get your dead times and small IPW comp set, remove the pulse dampers, the issue will likely be gone.

Thank you all for the help and advice. I got my idle fixed!

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